1. Field of the Invention
The present invention relates to disk drives, and more specifically, it relates to a disk drive which is connected to a host control unit through an interface such as a Universal Serial Bus (hereinafter referred to as xe2x80x9cUSBxe2x80x9d) interface and which controls the maximum current that flows through the disk drive, thus reducing the power consumption.
2. Description of the Related Art
In general, peripheral devices are connected to a host control unit such as a personal computer through a USB interface. The USB interface is for unifying connections of a personal computer with relatively low-speed peripheral devices such as a keyboard, mouse, modem, and printer by using the same type of connector and cable. Through a USB hub, many peripheral devices can be connected to a personal computer to form a star-shaped network. The USB connectors and USB cables are used to interconnect the USB hub and the personal computer and to interconnect the USB hub and the peripheral devices.
The power supply can be connected to the USB hub. The output of the power supply is supplied to the peripheral devices through the USB hub and the USB cables. Current that can be obtained from the power supply is limited by a characteristic of the USB hub, and generally the maximum current is approximately 500 mA.
Recently, a disk drive, particularly a floppy disk drive, has been connected to a personal computer using a USB-compliant connection. Specifically, the floppy disk drive is connected to the personal computer through the USB interface, and power for the floppy disk drive is obtained from the power supply connected to the USB hub.
When the floppy disk drive is connected to the personal computer using the USB-compliant connection, the maximum current available for the floppy disk drive is approximately 500 mA. In this case, the major current-consuming components of the floppy disk drive include a spindle motor for spinning a floppy disk and a stepping motor for actuating a head to move step by step. When the two motors are driven out of synchronization, the maximum driving current for each motor never exceeds a current limit of 500 mA. When the two motors are driven in synchronization, and when a starting current is introduced through the spindle motor, the sum of the two currents greatly exceeds 500 mA.
FIGS. 4A to 4D are waveform diagrams which illustrate examples of driving states of a stepping motor and a spindle motor in a conventional floppy disk drive. FIG. 4A illustrates the waveform of a step pulse signal. FIG. 4B illustrates the waveform of a stepping motor driving current. FIG. 4C illustrates the waveform of a spindle motor driving signal. FIG. 4D illustrates the waveform of a spindle motor driving current. The amplitude or current is plotted as the ordinate, and the time is plotted as the abscissa.
FIG. 5 illustrates a waveform when the starting current for the spindle motor and the driving current for the stepping motor of the conventional floppy disk drive overlap in time. The current is plotted as the ordinate, and the time is plotted as the abscissa.
As shown in FIGS. 4A and 4B, when a short-period step pulse signal is supplied to a stepping motor driving unit (not shown), the stepping motor immediately starts rotating step by step and actuates the head to perform a seek operation. A driving current which includes a low-amplitude fluctuating portion in the former half and a constant driving current in the latter half is directed to flow through the stepping motor. Neither driving current exceeds a current limit of 500 mA. When the supply of step pulse signals to the stepping motor driving unit is terminated, the stepwise rotation of the stepping motor stops, and the current returns to the initial value.
As shown in FIGS. 4C and 4D, when a spindle motor driving signal is supplied to a spindle motor driving unit (not shown), the spindle motor is activated. Upon activation, a starting current with a relatively high peak value flows through the spindle motor. When the spindle motor subsequently enters a steady rotation state, an approximately constant driving current flows through the spindle motor. The peak value of the starting current does not exceed a current limit of 500 mA.
As shown in FIG. 5, when the stepping motor is rotationally driven at a point at which the starting current starts flowing through the spindle motor, and when the driving current flows through the stepping motor, the starting current for the spindle motor and the driving current for the stepping motor overlap each other in time. The sum of the currents exceeds a current limit of 500 mA when the starting current for the spindle motor approaches its peak value. From this point onward, the sum of the currents continuously exceeds a current limit of 500 mA until the peak value of the starting current falls below a certain value.
In the conventional floppy disk drive, when the stepping motor and the spindle motor are not rotationally driven in synchronization with each other, the driving current for each motor does not exceed a current limit of 500 mA. However, when the starting current for the spindle motor and the driving current for the stepping motor overlap in time, the sum of the currents exceeds a current limit of 500 mA within a certain time range.
With respect to such a failure that occurs in conventional floppy disk drives, a floppy disk drive that aims to avoid such a failure is known.
When a stepping motor and a spindle motor are rotationally driven in synchronization with each other, the foregoing floppy disk drive stops the rotation of the stepping motor for a certain period of time from the time the spindle motor is started to be activated, that is, for a period of 250 to 500 ms which is approximately equal to a starting time of the spindle motor. As a result, a starting current for the spindle motor and a driving current for the stepping motor do not overlap in time, and hence the total current does not exceed a current limit of 500 mA.
In the above-described floppy disk drive, when the starting current flows through the spindle motor, the rotation of the stepping motor is stopped. As a result, the starting current for the spindle motor and the driving current for the stepping motor do not overlap in time, and hence the total current does not exceed a current limit of 500 mA. When a step pulse signal is supplied at a point at which the rotation of the stepping motor is stopped, the supply of the step pulse signal is ignored. When the stepping motor is reactivated after a stepping motor deactivation period, the rotational position of the stepping motor is deviated by a portion which corresponds to the ignored step pulse signal. Thus, the head cannot perform an accurate seek operation to a predetermined position, thereby causing a so-called seek error. The occurrence of such a seek error is prevented by somehow regenerating the ignored step pulse signal. If a device for regenerating a step pulse signal is provided, the configuration becomes more complex, and the cost is increased.
Accordingly, it is an object of the present invention to provide a disk drive for maintaining, without using an additional new component, the total current of the disk drive to be below a steady current limit without causing a seek error.
In order to achieve the foregoing objects, a disk drive according to the present invention is provided including a disk from and to which information can be read and written; a disk driving motor for spinning the disk; a read/write head disposed in the vicinity of the disk; a head transfer mechanism for transferring the read/write head in the radial direction of the disk; and a controller for controlling the entirety of the disk drive. When a step signal for driving the head transfer mechanism is output at a point at which the disk driving motor is activated, the controller immediately deactivates the disk driving motor and only actuates the head transfer mechanism to move step by step.
According to a disk drive of the present invention, when a disk driving motor (spindle motor) is activated at a point at which a starting current starts flowing through the disk driving motor, or when a step signal for driving a head transfer mechanism is output while the driving current is flowing through the disk driving motor, the rotation and driving of the disk driving motor is immediately stopped, and only a stepping motor which moves the head transfer mechanism step by step is rotationally driven. As a result, the total current of the disk drive is maintained to be below a steady current limit. Since part or the entirety of a supplied step signal never becomes invalid, no seek errors are caused. Thus, it becomes unnecessary to provide an additional unit for regenerating a step signal.
Preferably, the control unit reactivates the disk driving motor when the output of the step signal for driving the head transfer mechanism is terminated.
Accordingly, the disk driving motor which is once deactivated can be reactivated when the stepping motor stops rotating. Since a period in which a motor driving signal for rotationally driving the disk driving motor is supplied is longer than a period in which a step signal is supplied, the disk driving motor can be rotationally driven without supplying an additional motor driving signal.